The parts forming industry is one of the world's largest industries in both total revenue and employment. As a multi-billion dollar industry, even small improvements to the manufacturing process can prove to have an enormous efficiency and thus financial impact. Numerous methods and machines have been designed for forming parts. For instance, parts are generally formed via molds, dies and/or by thermal shaping, wherein the use of molds is presently the most widely utilized. There are many methods of forming a part via a mold, such as, for exemplary purposes only, stretch-blow molding, extrusion blow molding, injection blow molding, vacuum molding, rotary molding and injection molding.
One typical method of forming hollow containers is via a widely utilized process known as stretch blow-molding, wherein typically a three piece mold having two opposing side members and a bottom/push-up mold is utilized. Commonly, an injection molded preform, shaped generally like a test tube (also known as the parison), is inserted into the top of the mold. A rod is inserted inside the parison and is utilized to extend the parison to the bottom of the mold, upon which compressed air is forced into the parison, thus stretching the parison outward first toward the approximate center of the side mold members and then over and around the push-up/bottom mold. The parison is generally amorphous prior to initiating the blow process; however, after stretching the parison, the molecules align thereby forming a container having high tensile strength.
An even more popular method is the forming of parts utilizing a technique known as injection molding. Injection molding systems are typically used for molding plastic and some metal parts by forcing liquid or molten plastic materials or powdered metal in a plastic binder matrix into specially shaped cavities in molds where the plastic or plastic binder matrix is cooled and cured to make a solid part. For purposes of convenience, references herein to plastic and plastic injection molds are understood to also apply to powdered metal injection molding and other materials from which shaped parts are made by injection molding, even if they are not mentioned or described specifically.
A typical injection mold is made in two separable portions or mold halves that are configured to form a desired interior mold cavity or plurality of cavities when the two mold halves are mated or positioned together. Then, after liquid or molten plastic is injected into the mold to fill the interior mold cavity or cavities and allowed to cool or cure to harden into a hard plastic part or several parts, depending on the number of cavities, the two mold halves are separated to expose the hard plastic part or parts so that the part or parts can be removed from the interior mold cavity or cavities.
In many automated injection molding systems, ejector apparatus are provided to dislodge and push the hard plastic parts out of the mold cavities. A typical ejector apparatus includes one or more elongated ejector rods extending through a mold half into the cavity or cavities and an actuator connected to the rod or rods for sliding or stroking them longitudinally into the cavity or cavities to push the hard plastic part or parts out of the cavity or cavities. However, other kinds of ejector apparatus, such as robotic arms, scrapers, or other devices may also be used. Such ejectors are usually quite effective for dislodging and pushing hard plastic parts out of mold cavities, but they are not foolproof. It is not unusual for an occasional hard plastic part to stick or hang-up in a mold cavity in spite of an actuated ejector. One quite common technique is to design and set the ejectors to actuate or stroke multiple times in rapid succession, such as four or five cycles each time a hard plastic part is to be removed, so that if a part sticks or is not removed from a mold cavity the first time it is pushed by an ejector, perhaps it can be dislodged by one or more subsequent hits or pushes from the ejectors. Such multiple ejector cycles are often effective to dislodge and clear the hard molded plastic parts from the molds. Disadvantages of multiple ejector cycling, however, include the additional time required for the multiple ejector cycling each time the mold is opened to eject a hardened plastic part before it is closed for injection of a subsequent part and the additional wear and tear on the ejector equipment and the molds occasioned by such multiple cycling. Over the course of days, weeks, and months of injection molding parts in repetitive, high volume production line operations, such additional time, wear, and tear can be significant production quantity and cost factors.
On the other hand, stuck or incompletely ejected hard plastic parts can also cause substantial damage to molds and lost production time. In most injection mold production lines, the injection molding machines operate automatically, once the desired mold is installed, in continuous repetitive cycles of closing the mold halves together, heating them, injecting liquid or molten plastic into the mold cavities, cooling to cure or harden the plastic in the mold into hard plastic parts, opening or separating the mold halves, ejecting the molded hard plastic parts, and closing the mold halves together again to mold another part or set of parts. Very high injection pressures are required to inject the liquid or molten plastic into the mold cavities to completely fill all portions of the cavities in a timely manner, and such high pressures tend to push the mold halves apart during injection of the plastic. To prevent such separation of the mold halves during plastic injection, most injection molding machines have very powerful mechanical or hydraulic rams to push and hold the mold halves together. If a hard plastic part from the previous cycle is not ejected and completely removed from between the mold halves, the powerful mechanical or hydraulic rams will try to close the mold halves onto the hard plastic part, which can and often does damage one or both of the mold halves. Molds are usually machined very precisely from stainless steel or other hard metal, so they are very expensive to replace, and the down-time required to change them is also costly in labor and lost production. It is also not unusual for some of the plastic in a mold cavity to break apart from the rest of the part being molded in the cavity and remain in the mold cavity when the rest of the molded part is ejected. Such remaining material will prevent proper filling and molding of subsequent parts in the cavity, thus causing the subsequent molded parts to be defective. In automated production lines, substantial numbers of such defective parts can be produced before someone detects them and shuts down the injection molding machine for correction of the problem.
To avoid such mold damage, down-time, and defective molded parts as described above, various technologies have also been developed and used to sense or determine whether the hard molded plastic parts have indeed been dislodged and completely ejected or removed from the molds before the mechanical or hydraulic rams are allowed to close. Such technologies have included light beam sensors, vision systems, air pressure sensors, vacuum sensors, and others. U.S. Pat. No. 4,841,364 issued to Kosaka et al. is exemplary of a vision system in which video cameras connected to a vision system controller take video images of the open mold halves for computerized comparison to video images of the empty mold halves stored in memory to detect any unremoved plastic parts or residual plastic material in the mold halves. U.S. Pat. No. 4,236,181 issued to Shibata et al. is also an example of a vision system wherein photosensors are provided on a face plate of a CRT to electrically detect if a part has been removed.
As an improvement to the above systems, U.S. Pat. No. 5,928,578 issued to Kachnic et al. provides a skip-eject system for an injection molding machine, wherein the system comprises a vision system for acquiring an actual image of an open mold after a part ejector has operated and a controller for comparing such actual image with an ideal image of the open mold to determine if the part still remains in the mold. If so, the controller outputs an ejector signal to actuate the ejector to cycle again. Additionally, the patents to Kachnic et al., Kosaka et al. and Shibata et al. provide a means for inspecting the part for defects.
However, in view of the present system and method, the prior systems are disadvantageous. More specifically, the above systems have typically utilized charge coupled device (CCD) cameras positioned on the top or sides of the mold to acquire an image of the mold. This requires that the mold be completely opened before an image can be acquired, thus slowing down the inspection process. Moreover, due to the angle of the sensing device relative to the mold, a skewed image is acquired thereby resulting in decreased resolution of the image and increased inspection error.
Therefore, it is readily apparent that there is a need for a part-forming machine having an in-mold integrated vision sensor and method therefor that provides an image that is acquired at a relatively parallel angle from the sensor and thus provides more accurate detection resolution. It is, therefore, to the provision of such an improvement that the present invention is directed.